Place ham, cut-side-down, in a shallow baking pan; cover with aluminum foil. Bake in a preheated 325°F oven 15 minutes per pound (about 1¾-2 hours).
Meanwhile, in small saucepan over medium-high heat, combine root beer, orange juice, mustard, cayenne and orange zest. Bring to a boil; reduce heat and simmer until reduced by half (about 15-20 minutes), stirring occasionally. Stir in glaze packet; simmer 5 minutes. Remove from heat and set aside.
Remove ham from oven 15 minutes before end time. Increase oven temperature to 425°F. Remove foil from ham and pour glaze over ham. Continue baking, uncovered, remaining 15 minutes.